Weird error like tickets 8892 and 10811

I have run up against this bug before:

https://code.djangoproject.com/ticket/8892

Recently, it was updated to "duplicate of"

https://code.djangoproject.com/ticket/10811

The TL;DR is

Sometimes when you have models with O2O or FK you can lose data if the
models are saved in the wrong order.

I'm having a similar yet different issue, using Django 1.6.5

I have a Job model with subclasses

class Job(models.Model):
job_number = models.CharField("Job Number", max_length=20,
unique=True, db_index=True)
date_opened = models.DateField()
slug = models.SlugField(max_length=20, unique=True)
def save(self, *args, **kwargs):
if not self.slug:
self.slug = self.job_number
super(Job, self).save(*args, **kwargs)

class WorkshopJob(Job)
job = models.OneToOneField(Job, parent_link=True)
invoice_number = models.CharField("Invoice Number", max_length=30, blank=True)
reported_fault = models.TextField()


And here we see a similar result:

>>> j = WorkshopJob.objects.get(id=9)
>>> j
<WorkshopJob: 1234>
>>> j.date_opened
datetime.date(2014, 6, 26)
>>> j.invoice_number
u'123'
>>> j.findings
u''
>>> j.findings="The CPU doesn't work"
>>> j.findings
"The CPU doesn't work"
>>> j.save()
>>> j.findings
"The CPU doesn't work"
>>> j = WorkshopJob.objects.get(id=10)
>>> j.findings
u''
>>> j = WorkshopJob.objects.get(id=9)
>>> j.findings
u''
>>>


Is this expected behaviour?

Is this caused by having overridden the save method on the Job class
and then not following up with an overridden save method on
WorkshopJob?

As another example:

>>> j = WorkshopCivilJob.objects.get(id=9)
>>> j.findings
u''
>>> j.findings="data"
>>> j.findings
'data'
>>> j.save()
>>> j.findings
'data'
>>> x = WorkshopCivilJob.objects.get(id=9)
>>> x.findings
u''
>>> x == j
True
>>> j == x
True
>>> j.findings
'data'
>>> x.findings
u''
>>>

Now my brain hurts.

How can I fix this?

cheers
L.


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